<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body>
        <!-- 4个board -->
        <div id="board1" style="position: absolute; width:80px; height:10px; left:420px; 
        top:555px; background-color: cadetblue;"></div>
        <div id="board2" style="position: absolute; width:80px; height:10px; left:520px; 
        top:555px; background-color: cadetblue;"></div>
        <div id="board3" style="position: absolute; width:80px; height:10px; left:620px; 
        top:555px; background-color: cadetblue;"></div>
        <div id="board4" style="position: absolute; width:80px; height:10px; left:720px; 
        top:555px; background-color: cadetblue;"></div>
        <!-- 小球 -->
        <div id="ball" class="circle" style="width:20px; 
        height:20px; background-color:crimson; border-radius: 50%; position:absolute; 
        left:600px; top:100px"></div>
        <!-- 框 -->
        <div id="box" style="border: 5px solid #555555; width:400px; height:550px"></div>
        <!-- 分数 过的board越多，分数越高 -->
        <div id="score" style="width:200px; height:10px; position:absolute; left:900px; 
            font-family:'隶书'; font-size: 30px;">分数：0</div>
        <!-- 游戏结束 -->
        <div id="gg" style="width:200px; height:10px; position:absolute; left:550px; top:200px;
        font-family:'隶书'; font-size: 30px; display: none;">游戏结束</div>
        <script>
            // 设置box的样式
            var box = document.getElementById("box");
            box.style.position = "absolute";
            box.style.left = "400px";
            // 设置board的样式
            var board1 = document.getElementById("board1");
            var board2 = document.getElementById("board2");
            var board3 = document.getElementById("board3");
            var board4 = document.getElementById("board4");
            // 声音
            var shengyin = new Audio();
            shengyin.src = "声音2.mp3";
            shengyinFlag = 0; // 用来表示小球在第几块board上
            // 键盘事件函数
            var ball = document.getElementById("ball");
            document.onkeydown = f;
            function f(e){
                var e = e || window.event;
                switch(e.keyCode){
                    case 37:
                        // 按下左键，小球左移，但不要超过左边框
                        if(ball.offsetLeft>=box.offsetLeft + 10)
                            ball.style.left = ball.offsetLeft - 8 + "px";
                        break;
                    case 39:
                        // 按下右键，小球右移，但不要超过由边框
                        if(ball.offsetLeft<=box.offsetLeft+box.offsetWidth-ball.offsetWidth-10)
                            ball.style.left = ball.offsetLeft + 8 + "px";
                        break;
                    case 32:
                        
                }
            }
            // 定义一个分数变量
            var fenshu = 0;
            // 定义一个函数，移动给定的一个board
            function moveBoard(board)
            {
                var t1 = board.offsetTop;
                if(t1<=0)
                {
                    // 如果board移到最上面了，就随机换个水平位置，再移到最下面
                    t2 = Math.floor(Math.random() * (720- 420) + 420);
                    board.style.left = t2 + "px";
                    board.style.top = "555px";
                    fenshu += 1; //分数增加1
                    document.getElementById("score").innerHTML = "分数：" + fenshu;
                }
                    // 
                else
                    board.style.top = board.offsetTop - 1 + "px";
            }
            // 定义小球的速度变量
            var startSpeed = 1;
            var ballSpeed =startSpeed;
            // step函数是游戏界面的单位变化函数
            function step()
            {
                // board直接上下隔得太近，就逐个移动，否则，同时移动
                var t1 = Math.abs(board1.offsetTop - board2.offsetTop);
                var t2 = Math.abs(board2.offsetTop - board3.offsetTop);
                var t3 = Math.abs(board3.offsetTop - board4.offsetTop);
                // 定义一个board之间的间隔距离
                var t4 = 140;
                if(t1<t4)
                {
                    moveBoard(board1);
                }
                else if(t2<t4)
                {
                    moveBoard(board1);
                    moveBoard(board2);
                }
                else if(t3<t4)
                {
                    moveBoard(board1);
                    moveBoard(board2);
                    moveBoard(board3);
                }
                else
                {
                    moveBoard(board1);
                    moveBoard(board2);
                    moveBoard(board3);
                    moveBoard(board4);
                }
                // 定义小球的垂直移动规则，1、向下匀加速运动，2、如果碰到board就被board持续抬上去，
                // 直到按左右键离开了该board

                // 如果小球的纵坐标等于某个board的纵坐标，就被抬起
                var t5 = Math.abs(ball.offsetTop - board1.offsetTop);
                var t6 = Math.abs(ball.offsetTop - board2.offsetTop);
                var t7 = Math.abs(ball.offsetTop - board3.offsetTop);
                var t8 = Math.abs(ball.offsetTop - board4.offsetTop);
                if(t5<=ball.offsetHeight && t5>0 && ball.offsetLeft>=board1.offsetLeft-ball.offsetWidth && ball.offsetLeft<=board1.offsetLeft+board1.offsetWidth)
                {
                    ball.style.top = board1.offsetTop - ball.offsetHeight + "px";
                    ballSpeed = startSpeed;
                    if(shengyinFlag != 1)
                    {
                        shengyin.play();
                        shengyinFlag = 1;
                    }
                }
                else if(t6<=ball.offsetHeight && t6>0 && ball.offsetLeft>=board2.offsetLeft-ball.offsetWidth && ball.offsetLeft<=board2.offsetLeft+board2.offsetWidth)
                {
                    ball.style.top = board2.offsetTop - ball.offsetHeight + "px";
                    ballSpeed = startSpeed;
                    if(shengyinFlag != 2)
                    {
                        shengyin.play();
                        shengyinFlag = 2;
                    }
                }
                else if(t7<=ball.offsetHeight && t7>0 && ball.offsetLeft>=board3.offsetLeft-ball.offsetWidth && ball.offsetLeft<=board3.offsetLeft+board3.offsetWidth)
                {
                    ball.style.top = board3.offsetTop - ball.offsetHeight + "px";
                    ballSpeed = startSpeed;
                    if(shengyinFlag != 3)
                    {
                        shengyin.play();
                        shengyinFlag = 3;
                    }
                }
                else if(t8<=ball.offsetHeight && t8>0 && ball.offsetLeft>=board4.offsetLeft-ball.offsetWidth && ball.offsetLeft<=board4.offsetLeft+board4.offsetWidth)
                {
                    ball.style.top = board4.offsetTop - ball.offsetHeight + "px";
                    ballSpeed = startSpeed;
                    if(shengyinFlag != 4)
                    {   
                        shengyin.play();
                        shengyinFlag = 4;
                    }
                }
                else
                {
                    ballSpeed = ballSpeed + 0.01; // 数字相当于加速度
                    ball.style.top = ball.offsetTop + ballSpeed + "px";
                }
                // ballSpeed = ballSpeed + 0.01; // 数字相当于加速度
                // ball.style.top = ball.offsetTop + ballSpeed + "px";
                
                // 如果小球跑出来box，就结束游戏
                if(ball.offsetTop==0 || ball.offsetTop>=box.offsetTop+box.offsetHeight)
                {
                    clearInterval(gameover);
                    ball.style.display = 'none';
                    board1.style.display = 'none';
                    board2.style.display = 'none';
                    board3.style.display = 'none';
                    board4.style.display = 'none';
                    var gg = document.getElementById("gg"); //显示游戏结束
                    gg.style.display = 'block';
                }
            }

            var gameover = setInterval("step();", 8);
        </script>
    </body>
</html>
